As computers have evolved in processing capacity in recent year, there is expected for an image-using system for executing, for example, measurement and monitoring that was not easily realized until then due to the large amount and complexity of data to be processed thereby. In particular, with the use of conventional monitoring systems, there are many cases where video images sent from a monitor camera is verified through the human eye, so that there is expected to implement automation of the verification operation.
As one field in which such automation is expected, there is a scene of gas leakage from a coke oven in a steel making plant. In many cases, such gas leakage occurs from an oven lid, and is considered to result from causes, such as warpage of the oven lid due to high temperature, corrosion of a contact surface, and intrusion of foreign matters such as coal, coke, and tar. In recent years, ovens having a construction that is less likely to cause gas leakage have been developed. To date, however, no oven lids completely free from causing gas leakage over a long period of time have been available. When gas leakage caused due to continuation of operation occurs, stopping operation is carried out by the worker. In such a present situation, although gas leakage portions are repaired by necessity, detection of such gas leakage portions is carried out only by the worker. For such a coke oven that normally is used on a round-the-clock basis, there is expected to realize an apparatus capable of automatically detecting gas leakage from the oven lid. In this case, when an image of gas leakage is viewed by the human, the gas leakage can be found quickly or at one glance. An easiest way to find gas leakage from image information, an image captured under exactly the same conditions as a gas leakage image in regard to the weather of the day and the position of the camera can be subtracted from the gas leakage image, thereby a resultant image thus obtained shows only a gas leakage portion.
However, it is significantly difficult to create the same conditions in regard to the weather of the day, i.e., the illumination conditions. Since the illumination conditions are different from one another, when images are captured under different conditions, there remain portions other than the gas leakage portion.
Thus, when attempting to mechanically and quantitatively extract even such a change quickly recognizable to the human, a difference in image capture condition, such as an illumination condition, results in imposing a significant hindrance. As such, there arises the necessity of performing processing, such as correction, of the images to prevent the problem described above. Further, in many cases, image information is multidimensional as having density values R, G, and B of positions x, y, so that it is necessary to successfully acquire the image characteristics from the information.
In view of the circumstances described above, an object of the present invention is to provide an object monitoring method, an object monitoring apparatus, and an object monitoring program storage medium that are capable of accurately acquiring a change between two images by acquiring information of the images even when image capture conditions, such as illumination conditions, are different from one another in the events of capturing the images (one of the two images will be referred to as a “reference image”, and the other will be referred to as a “comparison image”, herebelow).